Dynamic thickness adaptation for an in-line scale

ABSTRACT

Methods and apparatus for weighing an article, such as a mail piece, while the article is moving at high speed. An article ( 900 ) is received from an intake transport ( 1200 ), and gripped in a weighing station ( 1310 ), in between a capstan roller and a pinch roller ( 1316 ), which are synchronized to minimize slipping. A first precision servo system ( 1252, 1250 ) alters the speed of the article, and in the process acquires torque data for storage and analysis ( 1212, 1282 ). A second precision servo system ( 1260,1330 ) applies a constant force, via a tension arm ( 1320 ), urging the pinch roller ( 1316 ) against the capstan roller, independently of the thickness of the mail piece. Active electronic damping ( 1900 ) reduces oscillation when an inconsistency in thickness of the article is encountered during weighing. The damping force is subtracted from the capstan motor torque data for improved accuracy (FIG.  20 B).

RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S.application Ser. No. 12/817,087 filed Jun. 16, 2010, entitled ACTIVEELECTRONIC DAMPING FOR AN IN-LINE SCALE, which is a continuation-in-partof co-pending U.S. application Ser. No. 12/562,798 filed Sep. 18, 2009,which is a continuation-in-part of U.S. application Ser. No. 11/855,130filed Sep. 13, 2007, now U.S. Pat. No. 7,687,727; each of which isincorporated herein in its entirety by this reference as though fullyset forth.

TECHNICAL FIELD

This invention pertains to methods and apparatus for accuratelydetermining mass-related properties of an article, such as weight ormoment of inertia, and more specifically it pertains to weighingarticles that are in motion.

BACKGROUND OF THE INVENTION

Many weighing systems are known, some dating back to biblical times.More recently, weighing systems have been developed for weighing eachone of a stream of articles, such as mail pieces or parcels movingthrough a transport or mail sorting system. Prior art systems of thattype are shown, for example, in U.S. Pat. Nos. 7,096,152 and 3,648,839.

Some known systems rely on back-EMF or “Electro Magnetic ForceRestoration” principles. According to one vendor, “an applied load iscompensated for by an electromagnetically produced counterforce. Aprecision position control (optical) keeps the system stable. Theslightest movement is detected, initiates a feedback circuit to runcurrent through a coil and causes the load to be returned to itsoriginal position. The coil current, which is proportional to theweight, is transmitted to an internal A/D converter then processed inthe microprocessor.”

Commonly-owned U.S. Pat. No. 7,687,727 discloses an improved in-linescale for very fast, accurate measurement of moving items such asmailpieces moving along a transport system. However, inaccuracies insuch measurements can result from variations in the thickness of theitems under measurement. The need remains for improvements in in-lineweighing systems.

SUMMARY OF THE INVENTION

In one class of embodiments, an article whose mass-related property isto be measured is presented, for example by entering a “weighingstation” via a transport mechanism such as a belt transport. Details ofsuch transport mechanisms are well known in various contexts, includingmail sorting machines. In alternative embodiments, the weighingapparatus might be used separately, for example in a machine arranged toapply the correct postage to a mail piece.

In some embodiments, a weighing apparatus in accordance with the presentdisclosure receives an article that has a measured or otherwise knowninitial state of movement (or rest). There is also a predetermined or“commanded” final state of movement (or rest) of the article. Andfinally, a mechanism is provided that applies an impulse to move theobject from its initial state to the commanded final state. (The term“mechanism” is used in this application in a broad sense. It is notlimited to purely mechanical contrivances; to the contrary, it refers toany and all mechanical, electrical, optical, electro-mechanical systems,software controlled systems, and combinations thereof that provide thedescribed functionality.)

The impulse-applying mechanism must include or be coupled to some meansof measuring or capturing information as a proxy for the actual impulse.In other words, the impulse typically is measured indirectly. Forexample, a curve of the torque that applies the impulse through a motorcan be used to infer sufficient information about the applied impulse.The measured proxy is then calibrated by articles of known mass-relatedproperties and the calibrated values are used to determine the article'smass-related properties. The use of calibration allows considerablesimplification to take place. As explained below, in a preferredembodiment, this approach obviates the need for actual or absolutemeasurements such as article velocity. Indeed, velocity is not criticaland need not be measured in absolute terms. One primary improvement ofthe present invention over prior art is that it allows weighing ofarticles at normal transport speeds; for example, hundreds of inches persecond for mail pieces.

In one embodiment, a method for weighing a moving article on the flycomprises the following steps:

-   -   receiving an incoming article having a first velocity;    -   without stopping the article, gripping the article between a        capstan roller and an opposed pinch roller;    -   synchronizing rotation of the pinch roller and the capstan        roller to avoid slippage of the article gripped between them;    -   providing a capstan servo motor having a shaft operatively        coupled to the capstan roller;    -   providing a first servo amplifier coupled to the capstan servo        motor so as to form a first closed-loop servo system for driving        the capstan servo motor and for monitoring torque applied by the        capstan servo motor;    -   in the first servo amplifier, commanding the capstan servo motor        to a predetermined, constant command speed that is different        from the first velocity of the article;    -   beginning after the article is gripped between the pinch roller        and the capstan roller, weighing the article on the fly by        acquiring a series of capstan servo motor torque sample data as        the article moves between the pinch roller and capstan roller,        so that the captured torque data reflects the torque applied by        the capstan servo motor to change the article speed from the        first velocity to the command speed;    -   storing the acquired torque sample data in a memory;    -   providing a second closed-loop servo system arranged for        controllably repositioning the pinch roller relative to the        capstan roller to apply a controllable gripping force on the        article as the article moves between the pinch roller and        capstan roller, wherein the second closed-loop servo system        provides an indication of a current position of the pinch roller        as the article moves between the pinch roller and capstan        roller;    -   detecting a change in the current position of the pinch roller        responsive to a change in thickness of the article as it moves        along still gripped between the pinch roller and the capstan        roller;    -   correcting the stored capstan servo motor torque data to remove        a torque error caused by the change in thickness of the article;        and    -   processing the corrected torque data to determine a weight of        the article independently of the actual speed of the article.

Additional aspects and advantages of this invention will be apparentfrom the following detailed description of preferred embodiments, whichproceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified electrical schematic diagram illustrating oneembodiment of a system for weighing articles on the fly.

FIG. 2 is a mechanical drawing in top view of an article transportapparatus including a weigh station in accordance with one embodiment ofthe present invention.

FIG. 3 is a mechanical drawing in top view showing greater detail of theweigh station of FIG. 2.

FIG. 4A comprises top view and cross-sectional views of an adjustablepinch roller assembly for use in the transport apparatus of FIG. 2.

FIG. 4B is a cross-sectional side view of a pivot roller assembly of atype useful in the weigh station of FIG. 2.

FIG. 4C is a side view of a pancake motor mounting in the articletransport apparatus of FIG. 2.

FIGS. 5-6 are mechanical drawings in top view illustrating a procedurefor replacing a pancake motor with a precision servo motor in theassembly of FIG. 2.

FIG. 7 is a side view illustrating a precision servo motor installedbelow a transport deck of a transport assembly with a sleeved hubinstalled for engaging an article moving through the transport assembly.

FIGS. 8A and 8B are oscilloscope traces of servo motor torquemeasurements taken in a development prototype weighing system inaccordance with one aspect of the present invention.

FIG. 9A is a top plan view of a transport assembly of a secondembodiment of an in-line weighing apparatus in a non-weighing state.

FIG. 9B is a top plan view of the transport assembly of FIG. 9A in aweighing state.

FIG. 10A is an exploded, perspective view of the transport assembly ofFIG. 9A.

FIG. 10B is an assembled, perspective view of the transport assembly ofFIG. 9A.

FIG. 11A is a top plan view of a transport assembly of a thirdembodiment of an in-line weighing apparatus in a non-weighing state.

FIG. 11B is a top plan view the a transport assembly of FIG. 11A in aweighing state.

FIG. 11C is an exploded, perspective view of the transport assembly ofFIG. 11A.

FIG. 11D is an assembled, perspective view of the transport assembly ofFIG. 11A.

FIG. 12 is a simplified electronic system diagram of a dual-servocontrolled in-line weighing apparatus in the context of a mail sortingsystem.

FIG. 13 is a side view of an embodiment of a dual-servo in-line weighingapparatus.

FIG. 14 is a top plan view the weighing apparatus of FIG. 13.

FIG. 15 is an enlarged top view taken along line 15-15 of FIG. 13showing drive linkage detail of the weighing assembly of the weighingapparatus of FIG. 13.

FIG. 16 is a perspective view of the weighing assembly with the deckshown in phantom.

FIG. 17 is a perspective view of a tension arm standing alone.

FIG. 18 shows sample measurement waveforms to illustrate an example ofweighing “on the fly” at a typical bar code sorter system transport beltspeed.

FIG. 19 is a simplified electronic system diagram of an example of animplementation of active, electronic damping for a tension arm servosystem in an in-line scale.

FIGS. 20A-20B present a series of signal graphs to illustrate operationof one embodiment of a weighing system in accordance with the presentdisclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning now to FIG. 1, a simplified electrical schematic diagram isshown illustrating one embodiment of a system for weighing articles onthe fly. In FIG. 1, a servo motor 110 is driven by a variable powersupply 120 which is coupled to a power source 122. In operation, currentflows through the motor to ground 124. A speed sensor (not shown) iscoupled to the motor 110 to provide a speed feedback signal 126. Varioussensors can be used such as shaft encoders, optical sensors, etc. toaccurately monitor speed or rotation of the motor 110. The speedfeedback signal is provided to an error amplifier 128, such as anop-amp, which compares the current speed to a predetermined input speedsetting 130. An error signal 132 related to the difference between thetwo inputs is input to the power supply 120 to control the motor currentthrough 110 so as to maintain the motor speed at the speed setting 130in the steady state. A change in the load on the motor, however, willresult in a transient in the motor torque indicative of that change inloading. That transient torque level may be captured as a proxyindicative of an impulse applied to the article.

Still referring to FIG. 1, the motor torque is monitored and a motortorque signal 140 related to the monitored torque level, for example adigital stream of samples, is input to a processor 142. This is notnecessarily a stand-alone processor, but it may be any programmabledigital processor, or a software component arranged to implement thedescribed functionality on a dedicated processor or as part of a largersystem. Article sensors 144, for example optical sensors (photodiodes,etc.), detect when each article of interest enters and leaves the weighstation, as further explained below with reference to other figures. Acalibration data store 148 stores calibration data, which can includesteady-state or “no load” measurements, taken when no article ispresent, as well as data taken from measurement of articles having knownmass. This data is used by the processor 142 to determine the articleweight, and the result is output, for example displayed, printed, orstored in digital file, as indicated at 150 in the drawing.

FIG. 2 is a mechanical drawing in top view of a belt-driven articletransport apparatus. In operation, articles move from right to left inthe drawing, from a first transport section, into a second transportsection (where a weigh station will be implemented as described below),and thence to a third or output transport section on the left. FIG. 3 isa mechanical drawing in top view showing greater detail of the secondtransport section of the apparatus of FIG. 2. Referring to FIG. 3,articles enter from the right through a variable pinch roller pair, pasta first photosensor, between a pair of fixed non-friction guides, andinto a first motor assembly. The first photo sensor, together withsecond and third photo sensors described below, generally correspond tothe article sensors 144 of FIG. 1. The first motor assembly comprises amotor driven hub, and an opposing spring-loaded pinch roller mounted ona pivot arm, controlled by a solenoid (not shown), for controllablymoving the opposing roller into contact or near contact with the saidhub so as to form a pinch roller pair for engaging the moving article.The first motor operates at the same speed as the belt-driven firsttransport section to normalize the speed of the article for articles ofdifferent lengths. Accordingly, each article enters the second transportsection at the same speed. The actual or absolute value of that speed isnot critical for present purposes. In contradistinction to prior art,the present system does not rely on speed measurements.

A second photo sensor detects movement of the article from the firstsection into the second section. The second section comprises a secondmotor assembly, similar to the first section. However, in accordancewith the present invention, the second section is modified by replacingthe common DC brush motor with a precision servo system furtherdescribed below. FIG. 4A comprises top view and cross-sectional views ofone example of an adjustable pinch roller assembly for use in thetransport apparatus of FIG. 2. FIG. 4B is a cross-sectional side view ofa pivot roller assembly of a type useful in the weigh station of FIG. 2.FIG. 4C is a side view of a pancake motor mounting in the articletransport apparatus of FIG. 2.

FIGS. 5-6 are mechanical drawings in top view illustrating a procedurefor replacing a pancake motor with a precision servo motor in theassembly of FIG. 2. The Teknic model M-2330 motor is just anillustrative example of such a servo motor. Other precision motors canbe used and should be considered equivalents. FIG. 7 is a side viewillustrating a precision servo motor installed below a transport deck ofa transport assembly with a sleeved hub installed for engaging anarticle moving through the transport assembly. Now we assume suchmodifications have been done, as described in the drawing, so that thesecond section motor assembly now employs a servo system in lieu of thepancake type motor used in the first and third transport sections. Athird photo sensor detects movement of the article from the secondsection into the third section. The third transport section (see FIG. 2)re-establishes the article speed to the system belt speed afterweighing.

Accordingly, in one embodiment, a transport mechanism (first section)projects an article at some initial velocity into the measuringapparatus. For example, in mail piece handling, a belt driven transportmechanism is commonplace. That velocity is known to the system itself(for such things as spacing the articles along their route), but itsvalue is not important and indeed is neither calculated nor used in theprocess of weighing the article. This ignorance by the weighingmechanism of the initial velocity of the article is material, since muchof the prior art measures mass by calculating the difference betweeninitial and final velocities of the article. Since the initial velocityis not provided to the weighing apparatus, such approach is precluded.

In one embodiment (see below for others) the article then enters ameasuring apparatus which pinches the article between two rollers. Inthe illustrative example in the drawings, the “measuring apparatus”generally corresponds to the second transport section, also referred toas a weigh station. The measuring apparatus has been commanded to outputthe article at a second velocity (which may be higher or lower than theinput velocity). This corresponds to the speed setting 130 of FIG. 1.The pinch rollers are driven by a servo mechanism (see FIG. 1) thatmeasures the angular velocity of a motor that drives one of the rollers,compares it to the desired angular velocity (at which the article wouldbe moving at the ordered output velocity), and supplies sufficienttorque to achieve the desired final angular velocity. The specificprofile of intermediate velocities ordered for or achieved by the systemare unimportant, though the proposed system includes devices thataccelerate and then decelerate the article (or the other way around) sothat its final velocity may be the same as its initial velocity. So, forexample, the weigh station may first accelerate, and then decelerate thearticle, arriving at the same velocity as the initial velocity, butgathering torque data in the meantime.

The solenoids that operate the pinch roller pivot arms are controlled sothat, while an article is in the second section (weigh station), asdetected by the photo sensors, the first and third transport sectionrollers are withdrawn from the motor hubs so that the weigh stationpinch roller assembly supports the article. In this way, accelerationand deceleration of the article are accurately reflected in the servoloop that drives the weigh station servo motor.

It is important to state that it does not matter what that final angularvelocity is. Unlike prior system, such as those disclosed on U.S. Pat.No. 7,096,152 or 3,648,839, the proposed system makes no absolutemeasurements at all. It works on calibration of torque, not absolutemeasurements of current or velocity.

The application of a precision instrument grade servo system to theproblem of weighing mail pieces or parcels while they are moving at ahigh speed enables multiple approaches to mass calculation. In apreferred embodiment, the servo mechanism is in continuous communicationand control of all of the moving roller system components prior tointroduction of the item to be weighed. In this way a state of nominalmotion or equilibrium can be established and related to the zero stateof the scale. (Recall zero state data can be stored in data store 148 ofFIG. 1.) Upon introduction of the subject article (which may be a mailpiece, a parcel, or other object), this equilibrium is disturbed.

The servo mechanism, by way of electronic and mechanical feedback loops,rapidly responds by injecting correcting signals to re-establish thenominal motion state. By measuring the error-correcting signalsgenerated by the servo system and scaling by a calibration factor, amass calculation can be made. Other methods of using servo data aredescribed later.

Since much of the prior art discusses calculating the weight (mass) ofthe articles, it bears mentioning here that the proposed system can workquite well with no actual calculation of article mass at all. All thatreally matters is the comparison of the mass-related property of thearticle to the mass-related properties of one or more calibrationarticles. Experimental data from a prototype is discussed later.

Other embodiments include but are not limited to the following:

-   -   Maintaining a state of angular momentum associated with the        nominal zero state and then measuring the incremental torque        required to re-establish the velocity of the nominal zero state        but now including an incremental mass (e.g. a mail piece).    -   Maintaining a nominal zero state of motion with an associated        constant torque and then measuring the difference in angular        displacement of the rotating components when an incremental mass        is introduced. The difference in angular displacement is        compared between the zero and the loaded state over equal and        fixed time intervals or over intervals whose ratio is known to        the system.    -   Maintaining a nominal zero state of motion with an associated        constant torque and then comparing the time differential        required to attain a fixed displacement.    -   Introducing an acceleration command and then measuring the        torque differential required to maintain that acceleration.

Non-linear relationships between the mass-related property of thearticle and the measured property are also envisioned by the proposedsystem. In such a case, sufficient calibration is required as toadequately define the relationships. It is not a requirement in everyembodiment that the article be propelled by a transport mechanism. Itcan for example, be self-propelled. In one embodiment, the object is atruck which moves at some measured velocity into the weighing apparatus.One possible system use is sorting the objects, such as mail pieces,into bins based on their determined weight (though this sortation is nota requirement of the proposed system). Another use may be to assesstaxes based on vehicle weight (for, say, a truck).

FIG. 9A is a top plan view of a transport assembly of a secondembodiment of an in-line weighing apparatus in a non-weighing state.This type of transport assembly may be integrated along a transporttrack of an automatic mail piece sorter machine, or the like, or may beimplemented in a stand-alone weighing machine. In general, a mail piece900 travels from left to right in the drawing. In FIG. 9A the mail piece900 is engaged between main transport belts 910 and 902 which movesynchronously at a predetermined system transport speed. This may be,for example, on the order of 150 inches per second. Belt 902 may bedriven and or guided by rollers 904, 906 etc. The left transport belt910 may be driven and or guided by rollers marked A, B and C forreference.

The left transport belt 910/902 conveys the mail piece 900 into aweighing station 950, further described below. After weighing, the mailpiece proceeds to exit the weighing station 950 by engagement in betweenright transport belt 918 and belt 902, again moving at the systemtransport speed. The right belt 918 is guided and or driven by rollersF, G and H as shown. These various belts are shown also in an explodedview in FIG. 10A. In the weighing station 950, the mail piece 900changes speed, perhaps more than once, but it does not stop. Thisexample has the advantage of maintaining a two-sided pinch to controlmail pieces as they travel through the system.

Turning now to the weighing station 950 in FIG. 9A, a front weigh belt960 is shown, driven by a motor 966 around a series of guide rollers L,M, N and O. The front weigh belt 960 is spaced apart from the mail piece900 in the non-weighing state shown in FIG. 9A. A rear weigh belt 940 isentrained on a series of guide rollers, generally as indicated, so thatbelt 940 also is spaced apart from the path of the mail piece 900 inthis non-weighing state. The weigh belts 940, 960 are spaced apart fromthe transport belts 902, 910, 914, 918 in the dimension into the page,so they do not conflict, as seen in the exploded view of FIG. 10A.(“Front” and “rear” are arbitrary labels in this description.)

FIG. 9B is a top plan view of the transport assembly of FIG. 9A in aweighing state. In this state, the mail piece 900 has entered the weighstation 950. The mail piece is disengaged from the transport belts asthe transport belts are repositioned into a weigh state spaced apartfrom the mail piece. To do so, guide rollers C, D, E and F are moved upas shown by the small arrows in FIG. 9B. Consequently, belts 910, 914and 918 do not contact the mail piece at this time. Rather, the mailpiece is now in contact with the rear weigh belt 940. In the lowerportion of the drawing, the lower transport belt 902 is not affected.Rather, in the weigh state, the front weigh belt 960 is repositioned tocontact the mail piece, so that the mail piece is gripped in between thefront and rear weigh belts only. To reposition the front weigh beltguide rollers M and N are moved upward, as indicated by the small arrowsin the drawing. The belt 960 thus moves the mail piece temporarily offof the transport belt 902 as further explained below.

The weigh belts are synchronized to the same speed, for example 250inches per second, which represents acceleration from the transport beltspeed (150 ips in the example). The weigh belts should be coupled to aprecision servo motor so that motion of the weighing belts translates toa corresponding rotation of the motor, and vice versa. In other words,there should be little or no slippage between the servo motor and theweighing belts. A separate motor may be coupled to each belt, as long asthe motors and respective belts are synchronized, or a single motor maybe used. Two motors are shown in the illustrated embodiment.

An example of a suitable servo motor is commercially available Teknicmodel M-2330. This is an instrument grade, brushless AC servo motor withintegrated encoder. Peak torque is on the order of 160 ounce-inches.Other precision motors can be used and should be considered equivalents.A high power density motor is preferred for building a weighing systeminto a confined space. The shaft encoder may provide, for example, onthe order of 4,000 to 8,000 counts per revolution.

As mentioned, FIG. 10A is an exploded view of the transport assembly ofFIG. 9A. In this view, a motor 946 drives the rear weigh belt 940. Asecond motor 966 drives the front weigh belt 960. A second (“lower”) setof front and rear weigh belts, 964 and 944, respectively, are shownbelow the transport belts 902 etc. These operate in the same manner asthe upper weigh belts 960, 940 as described. They should be synchronizedto the upper weigh belts, and may share common drive and controlelements. This may be termed an interleaved belt system, in that theweigh belts are above and below the transport belts.

FIG. 10B is an assembled, perspective view of the transport assembly ofFIG. 9A. Here is can be seen that the upper weigh belts (940,960) arelocated above the transport belts, and the lower weigh belts (arelocated below the transport belts. All three pairs of belts are sizedand spaced for engaging the mail piece 900—shown in dashed lines—at theappropriate times.

In operation of the assembly of FIGS. 9 and 10, a mail piece 900 isconveyed from left to right (FIG. 9A), initially by the transport belts.The intake transport belts are moving at a predetermined initialvelocity, for example the system transport speed in a sorter system, andthus the mail piece enters the weigh station at that initial velocity.Since the mail pieces may vary in length, for example from 5 inches to11.5 inches, short pieces would otherwise slow down before they hit themain rollers (weigh station) and produce a erroneous reading. To avoidthat result, the first pair of belts maintains the velocity of thesepieces, and then releases just as the piece reaches the main rollers.

Accordingly, when the mail piece arrives in the weigh station 950 (asdetected, for example, by photo sensors described later), the piece isreleased from the transport belts, and substantially immediately grippedin the upper and lower weigh belts (FIG. 9B), by the actions describedabove. This process may be enabled by a control system similar to theone described below.

In the weigh station, the piece may be accelerated and or decelerated bythe servo motor as discussed earlier to accomplish a weighing operation.The weigh belts thus change speed to make the measurement; the transportbelts preferably operate at constant speed. The piece then exits theweigh station, continuing to move from left to right in FIG. 9,essentially by reversing the above actions. That is, the assemblyswitches from the weigh state back to the non-weigh state. The weighbelts are disengaged from the mail piece, and substantially immediatelythe transport belts re-engage the mail piece. The mail piece may berestored to the initial velocity. In this way, a series of mail piecesmay move through the weighing station, and be weighed “in-line” withoutaffecting a larger system in which the weighing apparatus may beinstalled. Below we describe in more detail how the weight measurementsare electronically acquired.

FIG. 11A is a top plan view of a transport assembly of a thirdembodiment of an in-line weighing apparatus in a non-weighing state.Front and rear primary transport belts 1112 and 1102, respectively,convey a mail piece 1100 from left to right in the drawing. The mailpiece is gripped in between them, as shown, prior to weighing, and afterweighing. In this example, dimensions at 5-inch intervals are shown,based on an expected five-inch minimum mail piece length.

A second pair of transport belts 1122 front and 1120 rear, are arrangedto convey a mail piece, also at normal transport belt speed, when thesystem is not performing a weighing operation. The second transportbelts 1122, 1120 are spaced above the primary transport belts (as wellas the weigh belts), as best seen in the exploded perspective view ofFIG. 11C. The second transport belts “bridge the gap” in thenon-weighing state from the primary transport belts at the intake (left)side to the same belts at the output (right) side as the primarytransport belts are routed around the weigh station. This embodimentensures that even a 5-inch envelope is pinched between two belts at alltimes.

A third pair of transport belts 1130, 1132 (FIG. 11C) are sized andarranged like the second pair, but are instead located below the primarytransport belts. In other words, these belts are interleaved, as bestseen in the exploded view of FIG. 11C. That is, the second pair oftransport belts 1120, 1122 are located above the primary transportbelts, while the third pair of belts 1130, 1132 are located below theprimary transport belts 1102, 1112. All three pairs of belts are sizedand spaced for engaging the mail piece 1100 at the appropriate times(and not during actual weighing of the mail piece). The total height ofthe three belts, plus spacing, would be similar to the minimum expectedheight of a mail piece, for example a 3½ inch minimum for a standardletter. A pair of weighing belts 1114, 1116 are spaced apart from thetransport belts and not contact the mail piece in this non-weighingstate (FIG. 11A).

FIG. 11B is a top plan view of the transport assembly of FIG. 11A in aweighing state. The mail piece 1100 has moved into the weighing station.The mail piece is released from the primary transport belts, and alsoreleased from the second and third pairs of transport belts. The mailpiece is now gripped between the weighing belts 1114, 1116 for weighing“on the fly” i.e., without stopping its travel. To do this, rollers Pand Q are repositioned to relocate the rear weigh belt 1114, asindicated by two small arrows, to bring the belt 1114 into contact withthe mail piece. This also brings the opposite face of the mail pieceinto contact with the stationary front weigh belt 1116. The mail pieceno longer contacts any of the transport belts. Weighing is conducted asthe mail piece moves along gripped in between the weigh belts. Asbefore, the weigh belts are coupled to a suitable, precision servomotor.

The piece then exits the weigh station, continuing to move from left toright in FIG. 11, essentially by reversing the above actions. That is,the assembly switches from the weigh state back to the non-weigh state.The weigh belt 1114 is disengaged from the mail piece, and consequentlythe transport belts re-engage the mail piece. In particular, dependingon the size of the mail piece, the second and third transport beltsensure that the piece moves along into re-engagement with the primarytransport belts 1102, 1112 on the exit (right) side of the assembly. Themail piece may be restored to its initial velocity. FIG. 11D shows thetransport assembly in an assembled, perspective view, without a mailpiece.

FIG. 12 is a simplified system diagram of a dual-servo controlled,in-line weighing apparatus in a postal sorting system. This type ofsystem may be called “dual-servo” (or in some cases “2-axis”), as afirst servo loop controls a first servo motor for a weighing operation,and a second servo loop controls a second servo motor for grippingtension control during the same weighing operation. In the illustratedembodiment, a transport 1200, typically comprising moving belts, moves astream of mail pieces from right to left in the drawing. Such transportsmay move the mail at speeds on the order of 10 ft./sec although theparticular speed is not critical to this disclosure. We refer to thisquantity as the “system speed” or “transport speed.”

At the right or intake side of the drawing, a “PHOTO EYE #0” comprises alight source and a corresponding photo detector 1202, arranged to detectthe arrival of an incoming mail piece (not shown) as the leading orfront edge of the mail piece traverses the light beam. The resultingelectrical signal can be used to trigger a camera 1204 to start a newimage capture. The camera then uploads image data to an image captureand processing component 1214. This process preferably is implemented insoftware, and may be implemented in the ILS Processor 1212 in someembodiments. The image capture process 1214 stores the mail piece imagedata in a datastore 1218. In some embodiments, the system may be coupledto another database, e.g. an postal service ICS database, in which casethe image data may be stored there. After weighing, the ILS Processorstores the determined weight of a piece in the database 1218 inassociation with the corresponding image data.

The image capture process 1214 may utilize an OCR engine (software) 1216to extract or “read” a destination address, or at least ZIP code, fromcaptured mail piece image. These components may communicate over a localnetwork 1240, for example an Ethernet network. Destination address dataalso may be stored in 1218 in association with the item image or otheridentifying data. In an embodiment, ID Tag data from an ICS may be usedas an identifier.

Another database 1280 stores data for a batch of mail to be weighed inthe ILS. The database 1280 may include information about the mail piecesin the batch and the postage paid for mailing the pieces. The database1280 may include data or a machine-readable “manifest” provided by asender or pre-sort house. For example, it may have a list of the mailpieces in the batch. They may be listed individually, by destinationaddress, destination postal code, or using an internal ID number. Or,there may simply be a listing of the numbers of items, in total, or perzip code range, or per individual zip code. Other variations may beprovided by a mailer for its own internal purposes.

The database 1280 preferably includes postage information as well. Thismay be the actual amount of postage paid for each individual item, whereindividual items are listed. Alternatively, summary data may be usedwhere mail pieces are grouped or aggregated such that a bunch of itemshave the same postage paid. The database 1280 may include mailer permitinformation, postage rates, discounts, etc. Using this information, theILS Processor 1212 or another process can correlate the mail piecesreflected in the manifest in database 1280, with the weights of thecorresponding pieces, stored at 1218. It can determine the appropriatepostage for each piece, and compare the actual postage paid for thepiece. The difference, if any, is owed to the postal service (assumingthe subject mail piece is processed by the postal service). In someapplications, this system may be used to correct the postage for a batch(or individual items) before submission to the postal service.

Next we proceed to the weighing operations. After the envelope passes bythe camera 1204 (again, moving right to left in the drawing), a secondphoto detector pair (“PHOTO EYE #1) 1220 detects the leading edgeentering the in-line scale or weighing region. The photo detector 1220is coupled to a scale system controller 1230. A third photo detectorpair 1232, and a fourth photo detector pair 1234 also are coupled to thescale system controller 1230. Operation of these devices is describedbelow. The scale system controller 1230 may be connected by any suitabledata network arrangement, such as an Ethernet network 1240, forcommunication and data transfers with other components as indicated inthe drawing, and with the sorter system controller (not shown).

Referring again to FIG. 12, a first servo control system is driven bythe measurement servo controller 1250. The photo detector 1232 iscoupled to the measurement servo controller, as shown, to detect a mailpiece entering the weigh station. In addition, the photo eye detects thetrailing edge of the mail piece, which indicates that the piece hascleared the pinch roller #1 and therefore is ready for weighing. Themeasurement servo controller is coupled to a capstan motor 1252 forweighing operations. During a weighing operation, the mail piece isgripped between a capstan roller coupled to the capstan motor 1252, andan opposing pinch roller 1254. The pinch roller, in a preferredembodiment, is linked to the capstan roller to keep them synchronized.For example, in an embodiment, rather than a freewheeling pinch roller,the pinch roller 1254 opposing the capstan roller also is powered by thecapstan servo motor 1252. FIG. 13 illustrates such an embodiment,further described below. This arrangement increases the availablefriction surface area and reduces roller slippage to improve weighingaccuracy.

In addition, the weigh station pinch roller 1254 may be mounted on anactive swing arm assembly, as distinguished from a traditionalspring-loaded swing arm. Here, the swing arm (or tension arm) is coupledto a tension arm servo controller 1260. The servo controller preciselycontrols force applied to the tension arm as further explained later. Apassive spring system, by contrast, presents increased force (due toincreased spring compression) on thicker mail pieces. One example of anactive swing arm assembly is described below with regard to FIG. 13.

Two additional capstan and pinch roller assemblies provide speednormalization for mail pieces of varying length. A capstan 1266 andopposing pinch roller 1268 ensures that all mail pieces are presented tothe measurement rollers in the weigh station at uniform velocity.Another capstan 1270 and opposing pinch roller 1272 restores each mailpiece to the original transport speed. These capstans may be controlledby a speed controller 1274. These outboard pinch rollers may becontrolled (opened and closed) by the scale system controller 1230.

The controller coordinates their actions, based on input from the photodetectors, to grip a mail piece in the weigh station assembly (1252,1254), immediately after releasing it from the input side pinch rollerassembly (1266, 1268) or at substantially the same time as the piece isreleased, so as to minimize slowdown. Preferably, the grip in the weighstation is fast and firm, so as to minimize slippage in the rollers. Forexample, the force applied may be on the order of two pounds force. Inan embodiment, this gripping force is applied by the tension arm motor,under a precise servo control, and further described below. Slippage isalso minimized by synchronized, active drive of the capstan roller andthe pinch roller, rather than using a passive pinch roller. In anotherembodiment, a lesser gripping force may be applied. A system may beprogrammed to wait, for example on the order of 10 msec, to ensure thatthe piece has stopped slipping.

In one embodiment, the servo controller 1250 receives speed feedbackfrom the capstan motor 1252, and drives the motor as programmed. Forexample, it may be arranged to accelerate or decelerate the mail pieceby a predetermined amount. The servo loop must be fast and accurateenough to accelerate (and/or decelerate) a mail piece as commandedwithin a time frame that is practical for in-line applications. Suitableservo motors and amplifiers are described above. Preferably, weighing ofone piece is done within approximately 40 msec. The motor torque profileacquired during that acceleration can be analyzed to determine weight ofthe mail piece. The acceleration produces a spike or impulse in motortorque that may be captured and analyzed to determine weight. Bycontrast, a constant velocity in this scale would not work.

In other embodiments, mentioned above, the servo system may not seek toaccelerate or decelerate the piece to a new velocity. Rather, it mayinject an impulse to maintain a zero weight state.

FIG. 13 is a side view of an embodiment of an in-line weighingapparatus, installed on a platform or deck 1300 made of a sturdy, rigidmaterial such as steel. The deck may be, for example, on the order of1.0 cm thick, but this dimension is not critical. The deck surface mustbe substantially flat and smooth so as to provide a surface for mailpieces to glide over it without significant friction. A first roller(intake roller) 1302 is part of a capstan (1402) and opposing pinchroller pair, better seen in FIG. 14 top view. This is an intake rolleras a mail piece travels from left to right in the drawing, as indicatedby the arrow 1400 in FIG. 14. A similar output roller 1304 is again partof a capstan (1404) and pinch roller pair as shown in FIG. 14 in topview.

In operation, the intake capstan 1402 operates (CCW) at the same speedas a belt-driven transport section, if the weighing apparatus isinstalled in a larger machine such as a sorter, to normalize the speedof a mail piece for pieces of different lengths. This enables allincoming pieces to enter the weighing assembly at the same speed. Theactual or absolute value of that speed is not critical for presentpurposes. In contradistinction to prior art, this system does not relyon speed measurements. It is merely necessary that all articles arepresented to the weighing servo at identical speed regardless of length.

Referring again to FIG. 13, a weighing assembly 1310 includes a CapstanRoller, driven by a Capstan Motor 1312, via a shaft 1318 (see FIG. 16)which passes through the deck 1300. All the rollers (1302, 1402, CapstanRoller, Pinch Roller 1316, 1304, and 1404 are located above the deck1300 for conveying mail pieces (left to right) over the surface of thedeck. The various motors, gears and belts, described below, preferablyare located below the deck, leaving a clear path for the moving mailpieces. In another embodiment, some drive mechanics may be located abovethe deck.

Capstan Motor 1312 also indirectly drives an opposing Pinch Roller 1316(see FIG. 14), so that the Capstan Roller and Pinch Roller are preciselysynchronized. This minimizes roller slippage to improve weighingaccuracy. Referring now to FIG. 15, the Capstan Motor 1312, shaft 1318,drives Belt1, which in turn is linked to the opposing Pinch Roller 1316as follows. The Capstan Motor shaft 1318 (CCW) drives Belt1, which inturn drives a Gear1. Gear1 is mounted co-axially on a bearing on shaft1332 of the tension arm motor 1330, so that Gear1 is free to rotateindependently of the shaft 1332. An idler Gear2 is engaged with Gear1,so that rotation of Gear1 drives Gear2 clockwise, as indicated by arrowsin the drawing. Force applied by the tension arm motor 1330 does notaffect the operation of Gear1 or Gear 2. (The role of the tension armmotor is further described below.) See also the perspective view in FIG.16. Gear2, driven by Gear1 as noted, in turn is arranged to drive aBelt2 in CW rotation as shown in FIG. 15. Belt2 in turn is arranged torotate a pulley 1340, which is mounted to a shaft 1314 to drive thePinch Roller 1316.

Note the presence of a rigid tension arm 1320. The tension arm ismounted at one end on shaft 1332 of the tension arm motor 1330. Thetension arm 1320 supports the idler Gear2 which is mounted on a bearingfor free rotation. The other end of the tension arm, opposite thetension arm motor, comprises a generally cylindrical housing 1320(a),although the exact shape is not critical. Housing 1320(a) has a shaft1314 rotatably mounted therein, for example in a bearing assembly (notshown). The shaft 1314 extends upward through the deck 1300 to drive thePinch Roller. The shaft is driven by Belt2 by means of a pulley 1340mounted on the shaft 1314. FIG. 16 is a perspective view of theweighting assembly 1310, showing the deck in phantom for clarity. FIG.17 is a perspective view of the tension arm 1320 standing alone. Thisdesign is merely an example and not intended to be limiting.

In operation, the tension arm motor 1330 rotates the tension arm througha limited range on the order of approximately +/−10 degrees from aneutral or center setting. The exact range of motion is not critical.This rotation serves to adjust the position of the pinch roller 1316, asit is mounted to the tension arm as mentioned. An oblong slot 1315 inthe deck accommodates this motion (see FIG. 16). Because the CapstanRoller is fixed in position relative to the deck, repositioning thePinch Roller has the effect of adjusting the pinching force between theCapstan Roller and the opposing Pinch Roller, to keep it constant.

The tension arm motor 1330 preferably is driven by a precision servocontrol system, so that it provides a selected constant force on thePinch Roller. This feature is distinguished from other systems in whichpinch rollers generally are urged against the capstan roller by aspring. Springs provide a tension or force that varies with distance(compression of the spring). A spring therefore would cause the tensionin a mail system to vary with the thickness of each mailpiece,interfering with weighing operations as described herein. The systemdescribed above provides a constant force for gripping a mail piece inthe weighing apparatus independent of the thickness of the mail piece(within reasonable bounds). Note that tension arm servo controller datacan be used to record mail piece thickness if desired.

In one embodiment, a motion damper 1390 is fixed to the deck (see FIG.15) and arranged to apply a damping force to the tension arm to suppressvibration of the tension arm when it closes on a mail piece at highspeed. The damper shaft and piston are connected to the tension arm. Atension arm motion damper may be commercially available Ace Controls,model MA 225 or similar.

In a preferred embodiment, a capstan motor may be a commerciallyavailable servo motor such as Teknic model M-2311P or similar. Thecapstan motor may be controlled using, for example, a servo amplifiersuch as Teknic model SST-E545-RCX-4-1-3 or similar. In these amplifiers,also called servo drives, a high-speed DSP control processor controlsall of the feedback loops: position, velocity and actual torque. Torqueis actively measured and controlled, with losses in the motoreffectively minimized. The operation is substantially all-digital: themotor measurements are converted directly into digital format for theDSP and the outputs to the motor are digital PWM pulse streams. Inalternative solutions, analog processing may be used, as long as theperformance characteristics described herein are met.

The tension arm motor may be a commercially available servo motor suchas Glentek model GMBM-40100-13-0000000 or similar (Glentek, El Segundo,Calif.). This too is a brushless AC servo motor. It provides a 100 Wpower rating, 3000 rpm rated speed, and has a peak stall torque of aboutnine lb-inches. It may be controlled with a servo amplifier such asGlentek—SMA9807-003-001-1A-1 or similar. In operation, the servoamplifier can provide output data, in analog or digital form, thatindicates torque applied to the motor as a function of time.

In one embodiment, mail pieces travel into and leave the scale at aspeed on the order of 13 feet/second (156 inches per second). As noted,the exact transport speed is not critical. In a preferred embodiment,the system can calculate weight of each piece in real time. That leavesabout 70 msec available for each measurement. Within that time, a systemmay capture, for example, 128 sample measurements from the capstan servomotor amplifier. Weighing accuracy should be within a range ofapproximately +/−7 grams (0.25 ounce). Prototypes have demonstratedaccuracy on the order of +/−1 gram (0.035 ounce).

Active Tension Arm Damping

In some embodiments, the motion damper 1390 may succeed in dampingunwanted vibration, but it also slows the opening and closing of thespacing or “gap” between the capstan roller and the opposed pinch roller(1316). This can adversely affect operation in very high-speedapplications. Management of this gap is useful to higher speed weighingoperations. For example, in some embodiments, the tension arm motion maytake around 25 milliseconds to close on a mail piece. In some mailsorting systems, a 5-inch long mail piece represents a measurementinterval of approximately 53 milliseconds, so just closing the gap tobegin measurement takes up about half of the time available. Further,after measurement, the tension arm motion takes additional time to openthe gap for removing the item. The timing of the operation is furthercomplicated because of mail pieces (or other objects being weighed) thatvary in length from one piece to another.

One way to alleviate this problem is to reduce the mass of the tensionarm (1320). This may be done by modifying its design configuration, andor changing the material to a lighter material that still provides thenecessary strength, stiffness, etc. For example, some plastics or carbonfiber composites may be suitable. A lighter tension arm could berepositioned more quickly (other factors being roughly equal).

The mechanical damping described above is functional but it introducesproblems with gap management in some embodiments. The damper suppressesunwanted vibration during measurements, but it also retards opening thegap when a measurement is complete. Moreover, when a piece of varyingthickness is processed, weight may be miscalculated, again because thedamping interferes with the tension arm servo loop operation. Since thedamper resists opening the gap (rotating the tension arm), if a piecegets thicker say, half way through its measurement, the capstan servomust apply torque to open it. And yet, this extra torque has nothing todo with the weight of the piece. This problem may be called the “creditcard syndrome,” alluding to mail pieces that contain credit cards.

An alternative embodiment employs active electronic damping, instead ofusing a mechanical damper as described above. In this embodiment, thedamping function is controllable, and may be varied or switched on andoff, depending on the state of the weigh operation. The damping is ONduring weighing, i.e., when the tension arm is commanded to close. Whenthe tension arm closes to grip an article, various tolerances andelasticity in the system will lead to some “bounce” which is to say areversal in direction of the velocity of the tension arm. Moreover,repeated “bouncing” results in oscillation, all of which increase thetime necessary for the weighing apparatus to “settle” before accuratemeasurement data can be acquired. By damping the system, when closingthe tension arm, the settling time can be reduced, and thus thethroughput or speed of the weighing system increased. Ideally, we seekto critically dampen a tension arm servo system in order to minimize thesettling time.

Conversely, damping is turned OFF during reset, i.e., when retractingthe tension arm to open the gap. Accordingly, the gap will open faster.“Bounce” or oscillation when the gap is opened is not harmful. In someembodiments, desired damping can be accomplished by changing the mode ofthe tension arm servo and applying appropriate “PID” (proportional,integral, differential) settings for the tension arm servo feedbackloop. These are filter parameters of the well known digital PID-typeservo filter. The specific values (gain factors) are readily determinedby deriving coefficients for the equations of motion, but those valueswill vary with each particular system, and should be optimized for agiven design.

The active damping described herein may be implemented in various ways,including digital, analog, or mixed digital and analog solutions.Implementations may incorporate software executable on a suitableprocessor, or they may use hardware in the sense of dedicated electroniccircuits.

FIG. 19 is a functional illustration of one embodiment. The dashed box1900 represents an active electronic damping subsystem. A tension armservo amplifier 1902 (discussed above) provides a position output signalindicative of a present position of the tension arm (1320 in FIG. 13,for example). Because the capstan roller is fixed in position, thetension arm position signal is indicative of the relative spacing or gapbetween the capstan roller and the pinch roller. This position signalagain may be digital or analog, depending on the implementation. Forthis example, we proceed assuming an analog value (represented by acontinuously variable voltage level). A position signal 1903 is input toa suitable differentiator 1904, which in turn produces a velocity vector1905 (a quantity having a magnitude and sense or polarity). Wearbitrarily define a positive velocity as corresponding to moving thetension arm in the direction of closing the gap (between the capstanroller and opposed pinch roller). A positive torque command (at 1932)input to the servo amp 1902 results in positive velocity of the arm.

The velocity vector is input to a multiplier 1906. The multiplier 1906multiplies the velocity vector by a configurable damping gain factor.Preferably, the gain is selected (by calculation or empirically) tosubstantially critically damp the arm motion. When the arm “bounces”immediately after closing, the position signal change will result in anegative velocity vector (in the direction of opening the gap), and themultiplier 1906 will multiply or amplify that negative value, generatinga damping signal 1908. The signal 1908 is input to a switch 1910. Switch1910 is controlled by control signal 1912, provided by the multiplier1906, that reflects whether the velocity is positive or negative. If thevelocity is negative (reflecting a “bounce” motion of the arm), thecontrol signal 1912 controls the switch 1910 to connect the dampingsignal to a second switch 1920. If the velocity is positive (gap isclosing), switch 1920 remains open. The damping force in other words isinverted and scaled by the velocity generally in accordance with thefollowing equation:

$F_{d} = {{- {c\upsilon}} = {{{- c}\frac{x}{t}} = {{- c}{\overset{.}{x}.}}}}$

The tension arm controller 1260 generates an open/close binary swing armcommand as discussed above, labeled as signal 1922. (The terms “tensionarm” and “swing arm” are used interchangeably.) Command signal 1922controls the second switch 1920. If the command is to open the gap, thecommand signal drives switch 1920 to an open position, so that thedamping signal 1908, even if it reflects a negative velocity, is notcoupled to the summing junction 1930. Alternatively, when the commandsignal 1922 is to CLOSE the gap, then switch 1920 is closed to couplethe damping signal 1908 to the summing junction 1930. In this way,damping is enabled only when the tension arm is commanded to close.Conversely, no damping is applied when the command is to OPEN the gap,so the gap opens as quickly as possible. In the case of a mechanicalmotion damper, it cannot distinguish whether opening or closing iscommanded or occurring, and thus it slows all operations, retardingperformance.

Referring again to FIG. 19, the tension arm command signal 1922 is inputto a static torque setting circuit for selecting a pre-configured torquecommand setting, responsive to the OPEN or CLOSE command. A CLOSE armcommand as noted selects a positive torque setting. In that case,damping is enabled and switch 1920 is closed. Consequently, when the armbounces, and a negative velocity vector appears, the gain-multiplieddamping signal 1908 is connected via switch 1910 to switch 1920, andthence to the summing junction 1930. Note the inverting input (−)indicates that the damping signal is subtracted from the selected statictorque setting. Since the velocity vector is negative, this dampingsignal adds to the torque setting, so as to oppose or dampen the bounce.Illustrative signal graphs are described below with regard to FIG. 20A.

FIGS. 8A and 8B are oscilloscope traces of capstan servo motor torquemeasurements taken in a development prototype weighing system thatimplements aspects of the present invention. This data may be analyzedin various ways, for example using one or more suitably programmeddigital processors. Preferably, a real-time system determines a weightof a mail piece from the corresponding servo amplifier data quicklyenough that pieces can continue to move through the in-line scale atnormal sorting system speeds. For example, 128 servo samples over 30msec would require a data rate of around 4 k samples/sec.

FIG. 8A depicts a 5 gram differential torque measurement from a weigh onthe fly prototype. Trace “C” is 12 grams, “B” is 17 g and “A” is 22 g.Vertical scale is ounce-inches of servo motor torque and horizontal istime (on the order of 10 msec per division). The first vertical cursoron the left is the point at which the mail piece trips the photo eye forthe center roller (weighing) system. The other cursors are not relevant.It is straightforward to calibrate the system by weighing mail pieces ofknown weights.

FIG. 8B shows traces of 2.5 gram differential. The “E” line is 14.5 gand trace “D” is 17 g. These waveforms are of slightly different shapefrom the previous image due to increased oscilloscope gain and differentmechanical settings on the test bed transport. These traces show clearresolution even down to 2.5 grams. We believe this can be extended toconsiderably finer resolution while continuing to process at full speed(e.g. 40,000 pieces per hour).

In an embodiment, it is helpful to conduct a Fourier analysis on thetorque waveform sample data. The discrete Fourier transform (DFT) may beused to reduce the data to a small number of values or coefficients. TheDFT can be computed efficiently in practice using a fast Fouriertransform (FFT) algorithm. By pre-computing the same analysis on knowncalibration pieces, the Fourier coefficients of interest may be stored,for example in a lookup table, to determine weights later duringoperation by comparison to the values in the table. This approachprovides an effective way to compare the torque waveforms to provideaccurate measurements. It also helps to filter out vibration and othersystem noise from the measurement data.

In one embodiment, an in-line scale system of the type described abovemay be deployed within or in tandem with automated mail handlingequipment such as a destination bar code sorter machine (DBCS). On thebar code sorter system in this example, the transport belt speed is 153ips. The capstan servo on the ILS runs at 250 ips tangential velocity.The shortest mail piece is 5 inches long, plus a 3.5 inch minimum gapbetween pieces. So at an incident speed of 153 ips, we have ameasurement interval of approx 56 ms between pieces. This timing isillustrated in the upper trace of FIG. 18. The system therefore needs tocomplete all sampling and processing in this interval to operate in“real time”.

In a preferred embodiment, the system acquires 128 samples to the FFT,and the servo system described above samples at 1750 samples per second.This means that the sampling interval per piece is approx 73 ms.However, as noted, in the present example, only about 56 msec isavailable between pieces. One solution to this apparent dilemma is tosimultaneously sample into 2 separate measurements that are offset intime. The system thus is multi-threaded. We center the torque impulsedata for each piece in the 73 msec window so any data that appears insequential measurements is where the servo is quiescent or betweenpieces. This is essentially the zero area. This overlap technique isillustrated in FIG. 18. In the top figure, the time between the leadingedge of the impulses is 56 ms because the pieces are 5 inches longseparated by 3.5 inches. In the bottom figure, the pieces are 8 incheslong so the sampling overlap is smaller. The gap is constant at about3.5 inches.

Adapting for Thickness Variations

Variations in the thickness of an object being weighed, mentioned aboveas the “credit card syndrome,” can lead to measurement errors or reducedaccuracy in some situations. As discussed above, in a system with activetension arm damping, once the tension arm closes on an object, thedamper treats any movement away from the closed position as a bounce andacts to suppress it. The effect is that the capstan servo is required tosupply the torque needed to counteract the damping force, and thecapstan servo system reads this additional torque as force required toaccelerate mass, resulting in inaccurate weighing measurement.

This problem is illustrated in a series of signal graphs in FIGS.20A-20B. In the figures, the various signals are labeled from “A”through “J” for identification, and they are aligned temporally. (Thedrawings are merely illustrative; they are not exact or to scale.)Signal A represents tension arm torque command (see 1932 in FIG. 19). Itchanges state from OPEN command to CLOSE command at the appropriate timeto begin a measurement cycle. Signal B represents the tension armposition ideal; it moves to the closed position and remains in thatposition until the measurement is completed and the torque commandchanges to OPEN. Signal C represents the tension arm velocity ideal(derivative of the ideal position). Signal D illustrates the tension armactual position, indicating how it bounces when the arm closes on theobject (labeled “Hard Stop Bounce”) in the absence of active damping.(Signal D generally corresponds to a position output signal 1903 in theillustration of FIG. 19.)

The signal graph D also illustrates at 2010 a thickness inconsistency inthe object being weighed, which results in a change in the tension armposition. In this case, the arm opens as a thicker portion moves betweenthe pinch roller and the capstan roller (See FIG. 14). This thicknesschange results in corresponding pulses 2012, 2014, 2016 on signals E, Fand G, respectively, as illustrated in FIG. 20A. In signal G, the pulse2016 represents the damping force due to the thickness change. Morespecifically, the area of pulse 2016 equals (or is proportional to) thetotal damping force resulting from the thickness change.

Turning now to FIG. 20B, signal waveform H is essentially a duplicate ofsignal G from FIG. 20A for reference. Signal J illustrates the capstanservo motor torque including the error caused by the thickness change.Signal I shows the corrected capstan servo motor torque, determined bysubtracting the total force absorbed by the damping action(corresponding to the area of pulse 2018 on trace H) from the totalforce applied by the capstan. These calculations may be done, in oneembodiment, in the ILS Processor 1212 of FIG. 12. The resultingmeasurement data effectively ignores the inconsistency in thickness ofthe object. While only a single change in thickness has been discussedfor illustration, the systems and methods described herein would reactto additional changes, be they increases or decreases in thickness, insimilar fashion as such inconsistencies may be encountered.

Hardware and Software

Several examples have been described above with reference to theaccompanying drawings. Various other examples of the invention are alsopossible and practical. The system may be exemplified in many differentforms and should not be construed as being limited to the examples setforth above. The system described above can use dedicated processorsystems, micro controllers, programmable logic devices, ormicroprocessors that perform some or all of the operations. Some of theoperations described above may be implemented in software or firmwareand other operations may be implemented in hardware.

For the sake of convenience, the operations are described as variousinterconnected functional blocks or distinct software modules. This isnot necessary, however, and there may be cases where these functionalblocks or modules are equivalently aggregated into a single logicdevice, program or operation with unclear boundaries. In any event, thefunctional blocks and software modules or features of the flexibleinterface can be implemented by themselves, or in combination with otheroperations in either hardware or software.

Digital Processors, Software and Memory Nomenclature

As explained above, aspects of the invention may be implemented in adigital computing system, for example a CPU or similar processor in asorter system, in-line scale (standalone), or other embodiments. Morespecifically, by the term “digital computing system,” we mean any systemthat includes at least one digital processor and associated memory,wherein the digital processor can execute instructions or “code” storedin that memory. (The memory may store data as well.)

A digital processor includes but is not limited to a microprocessor,multi-core processor, DSP (digital signal processor), GPU, processorarray, network processor, etc. A digital processor (or many of them) maybe embedded into an integrated circuit. In other arrangements, one ormore processors may be deployed on a circuit board (motherboard,daughter board, rack blade, etc.). Aspects of the present invention maybe variously implemented in a variety of systems such as those justmentioned and others that may be developed in the future. In a presentlypreferred embodiment, the disclosed methods may be implemented insoftware stored in memory, further defined below.

Digital memory, further explained below, may be integrated together witha processor, for example RAM or FLASH memory embedded in an integratedcircuit CPU, network processor or the like. In other examples, thememory comprises a physically separate device, such as an external diskdrive, storage array, or portable FLASH device. In such cases, thememory becomes “associated” with the digital processor when the two areoperatively coupled together, or in communication with each other, forexample by an I/O port, network connection, etc. such that the processorcan read a file stored on the memory. Associated memory may be “readonly” by design (ROM) or by virtue of permission settings, or not. Otherexamples include but are not limited to WORM, EPROM, EEPROM, FLASH, etc.Those technologies often are implemented in solid state semiconductordevices. Other memories may comprise moving parts, such a conventionalrotating disk drive. All such memories are “machine readable” in thatthey are readable by a compatible digital processor. Many interfaces andprotocols for data transfers (data here includes software) betweenprocessors and memory are well known, standardized and documentedelsewhere, so they are not enumerated here.

Storage of Computer Programs

As noted, aspects of the present invention may be implemented orembodied in computer software (also known as a “computer program” or“code”; we use these terms interchangeably). Programs, or code, are mostuseful when stored in a digital memory that can be read by one or moredigital processors. We use the term “computer-readable storage medium”(or alternatively, “machine-readable storage medium”) to include all ofthe foregoing types of memory, as well as new technologies that mayarise in the future, as long as they are capable of storing digitalinformation in the nature of a computer program or other data, at leasttemporarily, in such a manner that the stored information can be “read”by an appropriate digital processor. By the term “computer-readable” wedo not intend to limit the phrase to the historical usage of “computer”to imply a complete mainframe, mini-computer, desktop or even laptopcomputer. Rather, we use the term to mean that the storage medium isreadable by a digital processor or any digital computing system asbroadly defined above. Such media may be any available media that islocally and/or remotely accessible by a computer or processor, and itincludes both volatile and non-volatile media, removable andnon-removable media, embedded or discrete.

It will be obvious to those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. The scope ofthe present invention should, therefore, be determined only by thefollowing claims.

1. A method for weighing a moving article on the fly, comprising:receiving an incoming article having a first velocity; without stoppingthe article, gripping the article between a capstan roller and anopposed pinch roller; synchronizing rotation of the pinch roller and thecapstan roller to avoid slippage of the article gripped between them;providing a capstan servo motor having a shaft operatively coupled tothe capstan roller and opposed pinch roller; providing a first servoamplifier coupled to the capstan servo motor so as to form a firstclosed-loop servo system for driving the capstan servo motor and formonitoring torque applied by the capstan servo motor; in the first servoamplifier, commanding the capstan servo motor to a predetermined commandspeed that is different from the first velocity of the article in orderto cause an acceleration of the article; beginning after the article isgripped between the pinch roller and the capstan roller, weighing thearticle on the fly by acquiring a series of capstan servo motor torquesample data as the article moves between the pinch roller and capstanroller, so that the captured torque data reflects the torque applied bythe capstan servo motor to change the article speed from the firstvelocity to the command speed; storing the acquired torque sample datain a memory; providing a second closed-loop servo system arranged forcontrollably repositioning the pinch roller relative to the capstanroller to apply a controllable gripping force on the article as thearticle moves between the pinch roller and capstan roller, wherein thesecond closed-loop servo system provides an indication of a currentposition of the pinch roller as the article moves between the pinchroller and capstan roller; detecting a change in the current position ofthe pinch roller responsive to a change in thickness of the article asit moves along still gripped between the pinch roller and the capstanroller; correcting the stored capstan servo motor torque data to removea torque error caused by the change in thickness of the article; andprocessing the corrected torque data to determine a weight of thearticle independently of the actual speed of the article.
 2. The methodof claim 1 including, in the second closed-loop servo system, activelydamping the relative motion of the pinch roller and the capstan rollerin order to reduce bouncing and capstan slippage while gripping thearticle.
 3. The method of claim 2 including disabling said damping whenmoving the pinch roller away from the capstan roller to release thearticle.
 4. The method of claim 2 wherein said actively dampingincludes: determining a velocity vector of the pinch roller positionresponsive to the indications of a current position; determining a senseof the velocity vector; and if the sense of the velocity vectorindicates that the pinch roller is moving away from the capstan roller,enabling said active damping.
 5. The method of claim 4 and furthercomprising: multiplying the velocity vector by a configurable dampinggain factor to generate a damping signal; and while said active dampingis enabled, adding the damping signal to a selected static torquesetting to generate a modified torque command for driving the pinchroller toward the capstan roller to grip the article, wherein saidadding step is configured so that the damping signal increases themagnitude of the selected static torque setting.
 6. The method of claim2 wherein said actively damping includes: providing a rigid tension arm;mounting the pinch roller to the tension arm; operatively mounting thetension arm to a tension arm motor for repositioning the tension arm andthereby repositioning the pinch roller relative to the capstan roller;driving the tension arm motor with the second closed-loop servo systemto control the applied gripping force while the article is weighed; andin the second closed-loop servo system, electronically damping thetension arm motion.
 7. The method of claim 6 including: in the secondclosed-loop servo system, receiving a tension arm command from acontroller; if the tension arm command is to close the tension arm,driving the tension arm motor to force the pinch roller toward thecapstan roller to grip the article; and if the tension arm command is toopen the tension arm, driving the tension arm motor to move the pinchroller away from the capstan roller to release the article, anddisabling the electronic damping.
 8. The method of claim 6 wherein saidcorrecting the stored capstan servo motor torque data includessubtracting an amount of torque attributable to the electronic dampingof the tension arm motion resulting from the change in thickness of thearticle.
 9. A weighing assembly for an in-line scale comprising: (a) acapstan roller; (b) a capstan motor operative coupled to drive thecapstan roller; (c) a pinch roller, positioned opposite the capstanroller and linked to the capstan motor for rotation in synchrony withthe capstan roller; (d) a first servo amplifier electronically coupledto the capstan motor and arranged to drive the capstan motor to aselected command speed of rotation, and to acquire torque data from thecapstan motor while a moving article is gripped between the capstanroller and the pinch roller; the torque data responsive to acceleratingor decelerating the moving article toward the command speed; (e) atension arm arranged for supporting the pinch roller while allowing freerotation of the pinch roller responsive to the capstan motor, and toenable repositioning the pinch roller; (f) a tension arm motoroperatively coupled to the tension arm, wherein the tension arm isarranged to translate torque applied to it by the tension arm motor toreposition the pinch roller relative to the capstan roller, therebyproviding a controllable gripping force for gripping the moving articlebetween the pinch roller and the capstan roller; (g) a second servoamplifier electronically coupled to the tension arm motor and arrangedto drive the tension arm motor responsive to a torque command input toapply a controllable force to the pinch roller while an article isgripped between the capstan roller and the pinch roller; wherein thesecond servo amplifier provides a position output signal indicative of acurrent position of the pinch roller as the article moves between thepinch roller and capstan roller; (h) an active electronic motion dampercoupled to the second servo amplifier to modify the torque command inputby a damping force responsive to a change in the position output signalso as to suppress oscillation of the tension arm when encountering achange in thickness of the article; and (i) a processor configured forprocessing the torque data acquired {provided} by the first servoamplifier to determine a weight of the article; (j) wherein theprocessor is further configured to correct the acquired torque data bysubtracting the damping force from the acquired torque data.
 10. Theweighing assembly of claim 9 wherein the active electronic motion damperis configured to dampen motion of the tension arm only when gripping anarticle between the pinch roller and the capstan roller.
 11. Theweighing assembly of claim 9 wherein the active electronic motion damperis implemented in a digital filter.
 12. The weighing assembly of claim 9wherein the active electronic motion damper is configured to enabledamping motion of the tension arm only when a velocity vector responsiveto the position output signal indicates that velocity of the tension armis negative.
 13. The weighing assembly of claim 9 and wherein theprocessor is arranged to determine the weight of the article bycomparing the corrected torque data to previously stored calibrationdata.
 14. The weighing assembly of claim 9 and wherein the processor isarranged to determine the weight of the article by applying a Fourieranalysis of the corrected torque data and comparing the results of theanalysis to previously stored Fourier calibration data.
 15. The weighingassembly of claim 9 and wherein the processor is coupled to the firstservo amplifier is configured to acquire two streams of capstan motortorque sample data from the first servo amplifier, the sample streamsoverlapping but offset in time.
 16. An in-line scale comprising: (a) afirst servo loop means for driving a capstan servo motor; (b) a capstanroller operative coupled to the capstan motor; (c) a pinch roller linkedto the capstan motor for rotation in synchrony with the capstan rollerand arranged adjacent to the capstan roller for gripping a moving objectreceived between the pinch roller and the capstan roller with minimalslippage; (d) a second servo loop means for driving a second servomotor, the second servo motor coupled to the pinch roller forcontrollably repositioning the pinch roller relative to the capstanroller so as to provide a gripping force for controllably gripping amoving object between the pinch roller and the capstan roller; (e) arigid tension arm coupled to the tension arm motor and supporting thepinch roller so as to allow free rotation of the pinch roller responsiveto the capstan motor, the tension arm arranged for translatingrotational force of the tension arm motor into forcing the pinch rollertoward the capstan roller to provide said gripping force; (f) an activeelectronic motion damping means coupled to the second servo motor tosuppress vibration of the pinch roller when it closes on an article togrip the article between the pinch roller and the capstan roller; and(g) electronic weighing means coupled to the first servo loop means fordetermining a weight of a moving object gripped between the pinch rollerand the capstan roller responsive to a torque applied to the capstanmotor; and wherein: (h) the electronic weighing means is also coupled tothe second servo loop means for detecting a change in thickness of amoving article gripped between the pinch roller and the capstan roller;and (i) the electronic weighing means is arranged to adjust the capstanmotor torque measurement by subtracting an amount of torque attributableto the active electronic motion damping means responding to the changein thickness of the moving article.
 17. The in-line scale of claim 16and wherein the active electronic motion damper means includes: inputmeans to receive a position signal; differentiator means fordifferentiating the position signal to generate a velocity vector; aconfigurable multiplier means for multiplying the velocity vector togenerate a damping signal; a command input to receive an open/closecommand signal; a static torque setting means for selecting a statictorque setting responsive to the command signal; and summing meansarranged for summing the damping signal and the selected static torquesetting for form a torque command input signal to the second servo loopmeans for damping bounce or vibration of the pinch roller only when thevelocity vector indicates bounce or vibration, and the command signalindicates close.
 18. The in-line scale of claim 17 wherein the summingmeans comprises: a first switch arranged to receive the damping signal;a second switch arranged to receive an output from the first switch; asumming circuit arranged to receive an output from the second switch andto sum the output from the second switch with a selected static torquesetting; and wherein the first switch is controlled by a sense of thevelocity vector to enable damping only when the sense of the velocityvector indicates that the pinch roller is moving toward the capstanroller; and the second switch is controlled by the command input toenable damping only when the command signal indicates close.
 19. Thein-line scale of claim 16 wherein the electronic weighing means detectsthe change in thickness of the article by detecting a change in thetension arm position signal or a change in the tension arm velocityvector.
 20. The in-line scale of claim 16 wherein the electronicweighing means is arranged to determine the torque attributable to theactive electronic motion damping means responding to the change inthickness of the moving article based on a tension arm torque commandinput signal provided by the active electronic motion damping means.